1. Field of the Invention
This invention pertains to subscription control of television programming which allows the subscriber to receive programming in preselected categories and programming on a pay-per-view basis. The invention is especially suitable for direct broadcast satellite (DBS) television applications.
2. DESCRIPTION OF THE PRIOR ART
Several techniques have been used in the prior art to facilitate pay-per-view operation in subscription television applications. Typically, when using such techniques, a broadcaster transmits a code identifying, with a unique address, each subscriber who has prepaid for the program. Each subscriber's control unit is enabled upon receiving the code. The control unit operates in conjunction with the subscriber's television receiver. It will be understood that when it is said herein that the control unit is enabled, the television receiver associated with such control unit also is enabled to the extent that it can receive the program. Similarly, when it is said herein that the receiver is enabled, it will be understood that the control unit associated with it has enabled it. Prior art devices, not having a memory associated with the control unit, require that each of the individual subscriber receivers must be enabled for each program. Consequently, it is necessary to enable the control units "between" different programs. For example, if viewer A subscribes to consecutive programs 1 and 2, his control unit must be enabled at the beginning of program 1 and remain enabled through the end of program 1. In addition, his control unit must be enabled to receive program 2 prior to the beginning of program 2. If viewer B subscribed to program 1 but not program 2, his control unit must be enabled prior to the beginning of program 1 and be disabled at the end of program 1 or very soon after the beginning of program 2.
In order to disable the subscriber receiving units automatically at the termination of a program, either an end-of-program message is transmitted to disable all subscriber units, or a timer, built into each subscriber's unit, is used to disable an associated subscriber unit.
This leaves a very small "window" in which time the broadcaster must transmit information to enable and disable all of those subscribers' control units.
Such prior art techniques require a high speed data channel for these addressing requirements. The prior art techniques usually are not suitable for direct broadcast satellite applications, since the very large number of subscribers would require an extremely large channel capacity for the addressing requirements. In addition, such techniques are vulnerable to program channel errors. That is, since the programming information is transmitted only once in a short time frame, if there are any problems with that transmission, such as a brief power failure at the subscriber's location, or adverse weather conditions such as a thunderstorm affecting the quality of the transmission, the subscriber's control unit may not be enabled. Conversely, if a "turn off" signal is not recorded in memory, a subscriber's control unit may remain enabled when it should be disabled. By repeating the subscriber programming information several times over a longer period, the likelihood of such errors may be reduced substantially.